Wei Jiaqi, Zhong Lixiang, Xia Huarong, Lv Zhisheng, Diao Caozheng, Zhang Wei, Li Xing, Du Yonghua, Xi Shibo, Salanne Mathieu, Chen Xiaodong, Li Shuzhou
Innovative Centre for Flexible Devices (iFLEX), School of Materials Science and Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore, 639798, Singapore.
Sorbonne Université, CNRS, Physico-chimie des Electrolytes et Nanosystèmes Interfaciaux, PHENIX, Paris, F-75005, France.
Adv Mater. 2022 Jan;34(4):e2107439. doi: 10.1002/adma.202107439. Epub 2021 Dec 2.
Ion adsorption inside electrified carbon micropores is pivotal for the operation of supercapacitors. Depending on the electrolyte, two main mechanisms have been identified so far, the desolvation of ions in solvents and the formation of superionic states in ionic liquids. Here, it is shown that upon confinement inside negatively charged micropores, transition-metal cations dissolved in water associate to form oligomer species. They are identified using in situ X-ray absorption spectroscopy. The cations associate one with each other via hydroxo bridging, forming ionic oligomers under the synergic effect of spatial confinement and Coulombic screening. The oligomers display sluggish dissociation kinetics and accumulate upon cycling, which leads to supercapacitor capacitance fading. They may be dissolved by applying a positive potential, so an intermittent reverse cycling strategy is proposed to periodically evacuate micropores and revivify the capacitance. These results reveal new insights into ion adsorption and structural evolution with their effects on the electrochemical performance, providing guidelines for designing advanced supercapacitors.
带电碳微孔内的离子吸附对于超级电容器的运行至关重要。根据电解质的不同，目前已确定两种主要机制：溶剂中离子的去溶剂化以及离子液体中超离子态的形成。在此，研究表明，当过渡金属阳离子溶解在水中并被限制在带负电的微孔内时，它们会缔合形成低聚物物种。通过原位X射线吸收光谱对其进行了鉴定。阳离子通过羟基桥相互缔合，在空间限制和库仑屏蔽的协同作用下形成离子低聚物。这些低聚物表现出缓慢的解离动力学，并在循环过程中积累，导致超级电容器电容衰减。通过施加正电位可以使它们溶解，因此提出了一种间歇反向循环策略，以定期排空微孔并恢复电容。这些结果揭示了离子吸附和结构演变及其对电化学性能影响的新见解，为设计先进的超级电容器提供了指导。
